1. Field of the Invention
This invention relates to a rocksaw device, and more particularly to a rocksaw disk capable of cutting a trench through hard rock on rocky soils.
The use of rocksaws in the art of trenching through hard rock and rocky soils has become practical through the introduction of the tungsten-carbide-insert tipped tooth held in a hardened steel socket at an angle to the direction of a cutting motion providing drag on the tooth point having an off-center component which induces rotation of the tooth in the socket.
This system is used in mining of relatively soft rocks, road planing, trenching, and sawing of hard rock.
The system requires tooth rotation to distribute wear evenly around the tooth point, keeping it sharp while at the same time dissipating the extreme heat generated by the friction between the rock and the carbide tip by rotating the heated tip portion out of the rock contact zone and providing a cooler tip portion in its place.
2. Description of the Prior Art
Conventional trenching devices comprise a driven disc or wheel on which tooth supporting segments are mounted. Each segment generally only covers a portion of the outer edge of the disc, e.g. 1/8 or 1/10, and a plurality of the segments are fastened to the disc to provide teeth around the entire periphery of the disc. A conventional mounting segment includes a base in the shape of a section of a toroid generated by a rectangle rotated around the disc axis. The base has radially inner and outer cylindrical section surfaces. The mounting segment also includes two segment mounting elements each having a plurality of holes therethrough for receiving bolts to attach the mounting segment to the disc. The base is attached to the segment mounting elements at its radially inner surface. The radially outer surface of the base is a mounting surface on which a plurality of tooth assemblies are mounted. The tooth assemblies are arranged in one or more patterns on each segment to provide teeth across a desired cutting width. Because the mounting surface is flat across its width in a direction parallel to the axis of the disc, the trench formed by the rocksaw also has a flat surface across the cutting width.
Each of the tooth assemblies comprises a tooth having a cylindrical shape with a central axis therethrough and a tungsten-carbide-insert tip at one end. A block having a bottom surface with a center line is welded to the segment base and rotatably supports the tooth at a constant rake angle defined between a line through the axis of the tooth and a line formed by the intersection of a first plane tangent to the segment base at the point where the block is attached and a second plane perpendicular to the first plane and including the line through the tooth's central axis.
The tooth blocks are arranged on each segment in a pattern to provide a desired cutting path during operation. The minimum cutting width of a cutting segment is set by the combined thickness of the disc plus the thickness of the segments bolted to it, the projection of fasteners, some extra width providing clearance from the trench side wall, and allowance for the shortening of cutter teeth through wear. In order to provide cutter teeth across the entire minimum width, the tooth blocks must be positioned somewhat crosswise to allow side clearance for the tooth assemblies and the disc and segment structure. This is accomplished by slanting and rolling the tooth assemblies on the mounting surface to provide side clearance of the tooth tip. Slanting comprises positioning a tooth block on the mounting surface to provide a slant angle, between the centerline of the bottom surface of the tooth block and a line tangent to the base at the point where the block is mounted to the base. Some slant is essential to induce rotation in the tooth tip. As discussed above, this distributes wear evenly around the tip and keeps the tip sharp. However, is the slant angle of a tooth is increased toward 90.degree., the advantage gained by side clearance of the tooth is obviated by problems such as severe side loading, overstressed welds, and broken tooth shanks.
Block roll is also employed to provide side clearance of the tooth tips. Roll is accomplished by welding a tooth block to the mounting surface at an angle defined by the intersection of a plane including the bottom surface of the tooth block and a plane tangent to the mounting surface at the point where the block is mounted on the surface. The use of roll increases the movement of the tooth tip to the side of the segment while reducing the top clearance of the tip. However, specialized welding is required to properly attach the block with a desired roll, thus, additional construction steps and specialized welding are necessary.
Any time either slant or roll, other than the slight amount of slant necessary for tooth rotation, is added to the tooth's designed in attack angle, it increases that angle and creates problems such as overstressed welds and broken tooth shanks. These problems are magnified when the speed of the disc and the power of the disc drive are increased to trench through hard rock and rocky soil.
Conventionally, segments have been crowded with teeth to minimize tooth breakage. The concept has been that by reducing the bite taken by each tooth, the strength of the rock would be overcome by the total strength of the teeth. However, increasing the number of teeth increases the forward force required to penetrate into the rock face being cut. Absent this increased forward force, penetration of the teeth drops and friction increases. This friction appears as heat at the interface between the tip and the rock. Since there is no shattering and removal of rock, the heat is retained in the contact zone and builds up with each passing tooth. This can result in excessive heat build up at the carbide tip causing softening of the cobalt matrix in which the carbide material is sintered. This, in turn, causes a radical reduction in the hardness and wear resistance of the tip. Therefore, it can be understood that crowding can be counter productive due to the decrease in the volume of material removed by a device delivering a constant forward force to the cutter teeth.
Another concern in conventional trenching device design is to balance the wear rate of the teeth across the width of the cutting segment.
The conventional trenching device cuts a trench having an essentially flat bottom and roughly square corners. The teeth positioned near the center of the cutting width have roughly 180.degree. of rock resisting chip formation while the teeth at the edges of the cutting width have about 270.degree. of rock structure applying resistance. This results in accelerated wear and breakage of the outer teeth. When this effect is combined with the above-mentioned effect of slant and roll of the outer segment teeth, the wear and breakage of these outer teeth is worse than the 180.degree. to 270.degree. rock resistance ratio would suggest.
The practice commonly followed to minimize uneven wear between the laterally outer and inner segment teeth has been to crowd the edges of the cutting width with additional tooth assemblies. As discussed above, crowding suffers from a counter productive trade off of balanced wear for cutter production. In addition, the use of extra tooth assemblies increases the cost of the device.
As can be understood, conventional trenching devices suffer from uneven wear of segment teeth across the cutting width and breakage of tooth and block welds. These problems are magnified when the device is used to cut hard rock or when the speed and horsepower of the device is increased.
It is desired to provide a device which minimizes these problems in a rocksaw capable of use in hard rock and rocky soil with high disc speeds and powers.